Paul Manafort, President Donald Trump's former campaign chairman, lied to investigators "on a variety of subject matters" and has breached his plea agreement, special counsel Robert Mueller's office said in a court filing on Monday.
The filing says Manafort does not agree with prosecutors' assertion that he has lied.
The filing was an astonishing break from the bare-bones updates given by the special counsel's office in other cases where cooperators continue to help Mueller pursue Russian interference in the 2016 United States election and alleged coordination with the Trump campaign.
Manafort pleaded guilty to conspiracy and witness tampering on September 14, nearly a year after he was first charged and following his conviction by a jury in a separate but related case on eight tax and banking crimes.
Manafort's legal team said he has "provided information to the government in an effort to live up to his cooperation obligations".
Mueller, who is also probing possible collusion between Moscow and the Trump campaign, said in the filing that after signing a plea agreement: "Manafort committed federal crimes by lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters".
Under an agreement with prosecutors, Manafort faces a maximum prison sentence of about 10 years, not counting a sentence for his August conviction in Virginia for bank and tax fraud.
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The move signals a return to the acrimonious relationship Manafort has had with the special counsel's office since his indictment previous year.
Mueller revealed the charge in a court filing Monday that indicated Manafort has violated the plea deal he made in the investigation by lying numerous times to the FBI.
Both sides asked Jackson to sentence Manafort without delay.
Trump has repeatedly denied collusion of any kind.
President Trump has branded the Mueller investigation a "witch hunt" and insisted there was no collusion between his team and Russian Federation.
He attended a meeting at Trump Tower in June 2016 with a group of Russians offering damaging information on Democratic candidate Hillary Clinton, who lost to Mr Trump in an upset in the presidential vote that November.
The apparent collapse of Manafort's cooperation agreement is the latest stunning turnaround in his case, exposing the longtime Republican consultant to more than a decade behind bars after pleading guilty in September on charges of cheating the Internal Revenue Service (IRS), violating foreign lobbying laws and attempting to obstruct justice.